1. Field of the Invention
The invention pertains broadly to a system for providing electrical power. More particularly, the invention is directed to an electrical power system particularly adapted for operation at remote sites.
Although its attributes lend it favorably to numerous applications, the invention is specifically adapted for continuous operation along a gas pipeline or at a gas well, providing electrical power for performing functions related to telecommunications, telecontrol, cathodic protection, supervisory control, data acquisition and remote gate valve sensing and activation in conformance with the International Natural Gas Pipeline Safety Regulations.
The remote sites associated with gas pipeline applications are typically characterized by harsh environments, including high temperatures, corrosive atmospheres and dusty air conditions. The latter factors present serious reliability concerns for power generation systems, contributing to high failure rates and high costs due to equipment repair and replacement. Moreover, the general remoteness of the power system along a gas pipeline or at a gas well, in conjunction with known reliability deficiencies, result in significant maintenance costs, arising from the inherent necessity for frequent maintenance visits to insure system integrity.
The relatively poor reliability of some conventional remote site power generators is particularly problematic in view of the criticality of the functions to be performed by the power system. Additionally, the probability of failure and future costly repair associated with some conventional remote site power generation systems present obvious negative financial implications relating to the life cycle costs for the system. Life cycle costs for a conventional system can be expected to increase, not only directly as a result of the costs of failure and repair, but also indirectly as a result of probable interruptions in the overall gas pipeline operation and support functions. The need to adopt a frequent maintenance scheme further contributes to high life cycle costs, severely limiting the utility of conventional power systems in remote site applications.
The remote power system of the present invention is uniquely characterized by low first cost, high reliability and efficiency, long life, low life cycle costs and minimal maintenance requirements over a 500 watt to 5,000 watt power output range. For loads between 500 and 5,000 watts, the low initial cost of the present power system makes it more attractive than competitive power generators. With its characteristic high efficiency, reduced maintenance costs and longer component lifetimes, the twenty-year life cycle costs for the subject invention are significantly lower than presently available conventional power generators. Furthermore, in gas pipeline applications, the power system of the present invention is adapted to derive its fuel directly from the natural gas pipeline, thereby affording almost-free fuel costs while eliminating related and often unpredictable fuel logistics costs.
The present invention is designed in conformance with the latest U.S. Military Reliability and Maintainability (R&M) 2000 Program, which emphasizes a "Back to Basics" approach for achieving superior reliability and easy maintenance in power systems through proven straightforward practical methods. In order to obtain a high level of reliability in combination with very low levels of maintenance, the recommendations of the International Telecommunication Union for the primary power supply of remote telecommunication systems are also incorporated into and, indeed, even exceed with the present remote power system design. Adhering to the fundamental design concepts of simplicity, ruggedness and internal redundancy, the remote power system is capable of providing the maximum possible energy availability to the load, while avoiding the high cost of field repairs.
Unlike other remote power sources on the market, the subject remote power system was developed to solve the problems of the user, and is therefore the first remote power product that is market driven rather than technology driven. Its characteristic high reliability and attractive life costing parameters address the requirements of the remote power system user, being perfectly adapted to gas pipeline applications. It is to be understood, however, that the invention is ideally suited to the entire remote site power system market where high reliability and minimal maintenance are essential, even where natural gas is not available and gasoline or diesel fuel must be transported to the site.
The remote power system of the present invention broadly includes a very slow speed heat engine directly coupled to an equally slow running oversized alternator. The engine is adapted to run on a variety of low BTU gases, preferably supplied directly from a gas pipeline. The slow speed of the engine, preferably around 600 RPM, results in low piston speeds and light bearing loads with very low wear rates.
The engine is adapted to be directly coupled to an oversized, equally slow speed heavy-duty brushless alternator which produces three phase AC at 30 Hz. The AC power is rectified to provide the desired DC voltage output for powering a station DC load in the range of 500 to 5,000 watts. The 500 to 5,000 watt range accounts for the majority of applications on new pipelines where multi-use stations are commonly employed to supply power for telecommunications, supervisory control and data acquisition, cathodic protection, and remote gate valve sensing and activation. The remote power system is capable of providing the entire 500 watt to 5,000 watt range in a single unit, thereby possessing a highly desirable expansion capability.
In accordance with the demands of the critical gas pipeline applications previously noted, the subject remote power system is adapted for continuous, twenty-four hour per day operation in harsh environments The invention is designed for six-month maintenance intervals with a comfortable margin.
The invention includes oversized lubricating oil tanks, oil filters, air filters and fuel filters to insure maximum cleanliness of the lubrication oil, combustion air and fuel for optimum engine performance and wear, thereby extending maintenance intervals to a minimum of six months.
The remote power system integrates fault tolerant design techniques to achieve unprecedented levels of reliability. In particular, internal redundancy is provided in critical areas, such as the provision of dual spark plug heads, high energy capacitive discharge solid state ignition systems, and redundant safety shutdown sensors and controls. Additionally, the invention utilizes a thermo syphon vapor phase type closed cycle cooling process. Moreover, sophisticated electronically activated controls are utilized to maintain precise optimum engine temperatures by controlling the electrical load and cooling system temperature so as to obtain maximum engine cleanliness, minimum engine pollutants, minimal engine wear, extended periods between routine maintenance visits and major overhauls, and greatly enhanced engine performance and life.
2. Description of the Prior Art
Several technical constraints serve to dictate the feasibility of power generating systems in gas pipeline applications. These technical constraints include remoteness of location, logistics of servicing and maintaining equipment, harsh environment, and need for reliability. The remote site locations typically affiliated with gas pipeline operations and similar remote locations make extension of the main power utility grid cost-prohibitive. Consequently, various technologies have been developed in an effort to provide cost-effective, reliable and easily maintainable power generating systems suitable for operation at remote sites in severe environments. The remote power technologies which currently receive general acceptance are the closed cycle vapor turbine, the high speed gas engine generator, the thermoelectric generator and the photovoltaic power system. Each of the presently accepted technologies exhibit numerous disadvantages in the 500 watt to 5,000 watt power range.
The closed cycle vapor turbine system is very inefficient, possessing an overall efficiency of only 3% to 4%. Hence, life cycle costs for such a system are prohibitively high, particularly for systems where power needs exceed 2,000 watts. Furthermore, the closed cycle vapor turbine relies on a vacuum to maintain rated output. Loss of vacuum through leakage or otherwise requires skilled personnel and sophisticated equipment to troubleshoot the cause and repair the deficiency in order to restore vacuum conditions. An even more serious potential problem affiliated with the closed cycle vapor turbine involves turbine seizure, requiring replacement of the approximately three hundred pound turbo alternator canister by personnel with the requisite expertise. The repair process frequently costs up to 30 percent of a new closed cycle vapor turbine. The present invention, on the other hand, is uniquely designed so that maintenance and repair tasks can be performed at the remote site by generally accessible and relatively unskilled personnel.
The natural gas high speed gas engine generator systems are also costly to maintain and operate. The high speed gas engine operates at 1800 RPM and, hence, is maintenance intensive, demanding frequent and costly maintenance protocols. All of the system's filters, fluids and tolerances must be professionally and carefully maintained within specified limits. Otherwise, the high stress levels will quickly cause major failures. The need for skilled maintenance becomes a serious problem at remote sites, where trained technicians are not likely to be readily available. In absence of monthly evaluation, the high speed engine is apt to deteriorate in a short time. Additionally, the high speed engine is generally incapable of withstanding continuous service in a hostile environment. Experience has shown that the systems tend to wear out quickly, culminating in frequent and expensive maintenance with random down times. The remote power system of the subject invention, in contrast, utilizes a slow speed engine to achieve reduced stress levels throughout the system with a drastic curtailment in maintenance requirements.
Although the overall reliability of a thermoelectric generator system may be high, the reliability of the system is sharply reduced in certain types of environments. Since the efficiency of the thermoelectric generator is directly related to the hot junction temperature, the system is deliberately designed to allow the hot junction temperature to come close to the thermoelement's maximum tolerable level. In view of the low inertia of the thermal system of the thermoelectric generator, any surplus heat is likely to bring the thermoelement into the danger zone very rapidly. The feasibility of the thermoelectric generator in high ambient environments is therefore compromised. Overheating is similarly likely to occur due to variations in the gas composition of the thermoelement caused by distillation of the light hydrocarbons in the gas or by a deviation from normal operating characteristics of the gas control components.
Another undesirable feature associated with thermal electric generators is that they are strictly limited to the peak rated capacity per individual thermoelectric generator module. Thus, in order to power larger loads, a number of units must be paralleled to arrive at the desired output capacity. Tee combination of multiple modules for greater output reduces the system Mean Time Between Failure by a factor equal to the number of generators utilized in the overall system. A multiple module power system is also more susceptible to overheating, as there is a greater likelihood that overheating of the thermoelement will ensue.
Each thermoelectric generator module is equipped with its own dedicated open flame combustion unit with control accessories and a very narrow cross-section burner orifice. This combustion system presents tee weakest link in an open flame thermoelectric generator. The combination of flameouts, orifice clogging, and internal pressure regulator variations are representative of ongoing reliability difficulties.
In contrast to the thermoelectric generator system, the remote power system of the present invention is characterized by a virtually unprecedented Mean Time Between Failure. Unlike the multi-module building block approach of the thermoelectric generator system, the invention is capable of providing from 500 to 5,000 watts output capacity without additional modules, equipment, or even adjustment. Indeed, since the parts count remains the same, a single unit is able to provide any amount of power over this range with the same high Mean Time Between Failure. Moreover, the invention does not require any sensitive energy conversion or combustion elements, nor does it employ any open flames.
Although a photovoltaic power system may be reliable and cost-effective for smaller loads, it too possesses a variety of technical disadvantages in the 500 to 5,000 watt output range. These disadvantages encompass allocation of physical space for the photovoltaic array, wind loading problems, and elaborate support structures and civil works requirements. The remote power system of the instant invention is free of the foregoing drawbacks, being relatively compact in physical size and of minimal complexity.
It is apparent from the preceding discussion that the need exists for a viable remote power system that is uniquely adapted for the 500 watt to 5,000 watt power output range, and which is specifically designed for highly reliable continuous operation at remote sites in harsh environments while requiring minimal and infrequent maintenance. The remote power system described and claimed in the present application addresses and fulfills this need by providing a remote power system which achieves essentially unsurpassed levels of reliability through a novel combination of components, gross derating of major subsystems, overall system simplification, and redundancy for key components.